Increased use of the Internet has continued to provide an impetus for higher communication rates. In the corporate realm, the need for high-speed access or data rates is often met by dedicated high-speed links (perhaps T1/E1 or T3/E3 frame relay circuits or dedicated lines) between a company and its Internet service provider (ISP). Users in the company typically utilize a local area network (LAN) to gain access to Internet routing infrastructure connected to the high-speed link. Unfortunately, residential users of the Internet are often not connected to such high-speed links, and frequently rely on standard analog or plain old telephone service (POTS) lines for access to the Internet.
The need to provide high-speed Internet access to residential consumer users is ever increasing due to the availability of information, entertainment, and the like through the worldwide web (WWW) portion of the Internet. For example, designers of web technology are constantly developing new ways to provide sensory experiences, including audio and video, to users of the WWW. As a consequence, higher-speed modems will be required to enable residential users to satisfactorily interact with the content and technologies being developed for the WWW. Unfortunately, analog or POTS line modems are limited by technical reasons to a maximum downstream data rate of 56 kilobits per second (Kbps). These conventional analog modems transmit and receive information on POTS subscriber lines through the public switched telephone network (PSTN). The Internet service provider is also coupled to the PSTN and transmits and receives information through it to the subscriber line.
A variety of communication technologies are competing to provide high-speed access to residential users. For example, DSL, cable modem, satellite broadcast, wireless LAN, and fiber technologies have all been suggested. Of these approaches, only DSL technology can utilize existing POTS subscriber lines between residential users and the telephone company central offices or local exchanges.
DSL technology provides a physical layer protocol for communicating information across a POTS subscriber line at data rates far exceeding those achievable using conventional analog modem technology and other physical layer protocols. One form of DSL is asymmetric digital subscriber line (ADSL) communication. ADSL communication involves transmitting data in one direction (typically downstream, or towards the customer premises) at a greater data rate than data is transmitted in the other direction (typically upstream, or towards the local exchange). There are also other known forms of DSL such as symmetric DSL (SDSL), high-speed DSL (HDSL) and very high-speed DSL (VDSL). These various forms of DSL are referred to generally herein as xDSL.
xDSL communication systems are generally implemented using a digital subscriber loop access multiplexer (DSLAM) located at a central office or other subscriber loop termination point of the PSTN. A DSLAM typically contains a number of xDSL termination units, or modems, that can establish an xDSL link and communicate xDSL protocol data across POTS subscriber lines. The xDSL termination units can be connected to the POTS subscriber lines via splitter devices that separate the xDSL data traffic from voice traffic on the telephone lines. Because an xDSL modem operates at frequencies higher than the voice-band frequencies, use of a splitter enables an xDSL modem to operate simultaneously with a voice-band modem or a telephone conversation over the same subscriber line. A splitter is similarly used at the customer premises to separate voice and xDSL data traffic and to provide the xDSL data traffic to an xDSL termination unit located at the remote customer premises. Once established, the xDSL link allows high-speed data communication to occur between the local exchange and the “customer premises equipment” (CPE) located at a remote customer site in the communication system.
The CPE typically includes an xDSL interface component that has an xDSL termination unit for terminating the xDSL link, as well as a buffer or other interface component between the xDSL termination unit and other CPE components. The xDSL interface may be implemented, for example, in the form of a network interface card (NIC) that interfaces between the xDSL link and a bus on a personal computer, workstation or other computing device. The xDSL interface can also form a component of a network router or bridge, such as an Ethernet or Universal Serial Bus (USB) router or bridge.
The xDSL physical layer may support various types of higher-layer user traffic, often concurrently. For example, user traffic may be carried in an asynchronous transfer mode (ATM) in which ATM cells carry user traffic. The xDSL physical layer may also support the transport of user traffic in a frame relay mode. In the frame relay mode user traffic is carried using frames formatted in accordance with the high-level data link control (HDLC) or other frame-based standard. User traffic may also be transported over the xDSL physical layer by being encapsulated within an Ethernet packet, which in turn may be carried within ATM cells or HDLC frame relay packets or some other packet delineation function which maps the bits of the packet to the physical xDSL bitstream. Additionally, many large consumer DSL service providers further encapsulate user traffic within Point to Point Protocol (PPP) packets, primarily for the purpose of limiting access to the network to only their paying customers. User traffic may be contained in packets formatted consistently with even higher network protocol layers, such as IP packets. As is known, IP packets may be routed through the Internet or a private IP network. For purposes of the following discussion, IP packets may be considered to encompass both Transmission Control Protocol IP packets (TCP/IP) and User Datagram Protocol IP packets (UDP/IP).
Turning now to FIG. 1, a block diagram is provided of an exemplary telecommunications system 10 containing a DSL-based access network 11. As shown, a plurality of subscriber locations 12 are connected to a network access provider (NAP) 14 over a corresponding plurality of xDSL links 16. The NAP 14, via a wide area network (WAN) 18 (or metropolitan area network (MAN)) which may or may not be owned by the NAP 14, is in communication with one or more Internet service providers (ISP(s)) 20 capable of handling voice and/or data traffic. The WAN 18 may be implemented as, for example, an ATM network, a frame relay network, an Ethernet network, or a native Internet Protocol (IP) network. In the cases where the WAN 18 consists of a non-native IP network, IP packets are transported over the applicable lower-layer networking technology (e.g., ATM, frame relay, Ethernet, or other networking technology).
NAP 14 represents an entity that (i) terminates xDSL link 16 at a central office or other subscriber loop termination point, and (ii) provides access to higher-level voice and data services offered by the ISP(s) 20. It should be understood that NAP 14 and the ISP(s) may or may not be affiliated or under common control. For example, a regional Bell operating company (RBOC) could provide both xDSL service and data-based Internet access, in which case it would maintain the role of both NAP 14 and ISP 20. Alternatively, in what is commonly called a “wholesale” DSL service arrangement, the NAP 14 and the ISP(s) 20 are completely separate commercial entities; the NAP 14 provides wholesale access to xDSL subscribers in return for a fee paid to it by the ISP(s) 20, and the ISP(s) 20 sell the retail Internet access service to the xDSL subscribers and collect money from them.
In operation, the NAP 14 receives packets and/or cells of voice and data information from the xDSL links 16. The NAP 14 forwards information from the received packets and/or cells to the WAN 18, which delivers such information as appropriate to the ISP(s) 20. It should be clear that information transfer occurs in the reverse direction from the ISP(s) 20 via the WAN 18 and the NAP 14. In this way the system 10 transports packets and/or cells of voice and data information between the subscriber locations 12 and the ISP(s) 20.
Each subscriber location 12 includes customer premises equipment (not shown) capable of effecting voice and/or data communication over its xDSL link 16. For example, such equipment may comprise an xDSL interface for transferring packets and/or cells of voice information to and from one or more voice-based communication instruments (e.g., telephones), and/or for providing packets and/or cells of data to a data subsystem (e.g., a personal computer, computer workstation or other computing device).
FIG. 2 illustratively represents an exemplary configuration of equipment utilized by the NAP 14. As shown, the NAP 14 utilizes one or more DSLAMs 26 located at a central office 28 or at an outside plant location or other facility positioned near enough subscriber locations 12 to enable xDSL transmission to be effected over xDSL links 16. Each DSLAM 26 is designed to support high-bandwidth applications over existing subscriber lines (i.e., the xDSL links 16). In operation, each DSLAM 26 performs adaptation between the xDSL links 16 and the WAN 18. In the downstream direction (i.e., towards the subscriber locations 12), each DSLAM 26 may perform switching and demultiplexing of packetized user information and/or ATM cells received from the WAN 18 over high-speed line 30. In the upstream direction (i.e., towards the WAN 18), each DSLAM 26 may perform multiplexing and concentration of packetized user information and/or ATM cells received over the xDSL links 16 for transmission on high-speed line 30.
In a very common implementation, such as that used by U.S. RBOC's for their consumer DSL services, the DSL-based access network 11 is configured to provide ATM cell transport from the subscriber locations 12 to the ISP(s) 20. In this regard the transported ATM cells serve as the layer-2 network protocol for establishing switched connectivity between these network nodes. Information formatted in accordance with higher level network protocols, such as Ethernet, PPP and TCP/IP packets, is encapsulated within the ATM cells and is communicated via ATM-based “virtual circuits”. In particular, each subscriber location 12 may be permanently assigned a virtual circuit extending from CPE (not shown) therein to an ATM switch or gateway router within the WAN 18. This logical circuit is defined at the layer-2 protocol level.
A major drawback of this type of Layer 2 ATM-based virtual circuit switching architecture is that it results in a proliferation of virtual circuits in the access network 11, since there exists at least one ATM virtual circuit for each DSL circuit. In fact, ATM was originally designed to support networks having substantially fewer endpoints and virtual circuits than existing DSL broadband networks. Since each virtual circuit is required to be scheduled and shaped in order to maintain a desired quality of service (QoS), scalability becomes difficult and expensive, both in provisioning and management as well as in equipment capacity. In this regard it is not unusual for ATM switches and ports on such switches to reach virtual circuit capacity long before reaching cell-forwarding capacity. Moreover, providing differentiated QoS in an ATM-based context requires that different services be furnished over different virtual circuits. This renders it rather expensive to scale a broadband network based upon this architecture, since it requires a different virtual circuit to be provided for each specific service desired by each individual subscriber. Finally, all data traffic entering a virtual circuit does not, by definition, emerge until it reaches the other end of the virtual circuit. That is, all traffic entering a virtual circuit is required to traverse the entire virtual circuit, irrespective of the ultimate destination of such traffic. This disadvantageously constrains the usage of IP and other higher-layer networking schemes within the access network, which may result in inefficient bandwidth usage and traffic patterns.
To overcome these drawbacks, it is desirable to introduce higher-layer network functionality, in particular IP networking, routing and QoS functionality, into these access networks. However, attempts to introduce and manage IP routing within access networks face a number of other challenges. For example, it is anticipated that direct use of IP addressing techniques within existing access network configurations would be rather inefficient. As is known, IP routing involves the forwarding of IP packets between different IP subnets. When using IP routing in a conventional access network, relatively large IP subnets are allocated to each central office facility. Subscriber addresses are then assigned from these subnets typically by dividing the larger IP subnet into smaller IP subnets, one for each subscriber. However, the addresses within each subnet must be allocated in blocks whose sizes must be powers of two, and every subnet requires reservation of two addresses (i.e., a subnet address and a directed broadcast address). This poses particular problems for small subscribers requiring public IP addresses, since it has become increasingly difficult to obtain new public IP addresses from the remaining public address pool. For example, if a given subscriber needs two IP addresses, a “/30 subnet” containing four IP addresses must be allocated because two of the four addresses are consumed by the full subnet and directed broadcast addresses. The term “/30 subnet” indicates that 30 of the 32 bits included within the IP address field are used to identify the subnet, with the remaining 2 bits being used in defining the 4 IP addresses of the subnet. If a subscriber simply needs 3 IP addresses, a /29 subnet consisting of eight IP addresses must be allocated. This inefficiently wastes three IP addresses, as well as the two addresses consumed by the full subnet and directed broadcast addresses.
FIG. 3 illustrates an access network in which an IP subnet has been established between the central office facility (CO) of a NAP and an Internet Service Provider (ISP). Specifically, in the case of FIG. 3 the 4-address subnet 192.168.5.0/30 resides between an IP router affiliated with the ISP and the CO. The network communication equipment within the CO uses 192.168.5.2 on its WAN interface, which causes the IP router to forward packet traffic to that WAN interface using 192.168.5.1. Within the CO, subscriber IP addresses are assigned out of two subnets, i.e., 192.168.0.1/24 and 192.168.1.1/24, each of which contain 256 IP addresses. These large subnets are then further subdivided among the subscriber interfaces. It is then necessary to have routes configured in both the ISP's IP router and the NAP's CO equipment in order to route traffic between the subscribers and the network. Such a configuration disadvantageously requires coordination between the ISP and the NAP, which are generally unrelated entities.
The arrangement of FIG. 3 also requires IP addresses to either be statically provisioned into the NAP's IP devices, or dynamic routing protocols (which are often troublesome to administer and troubleshoot) must be employed to share route tables. Either way, coordination between the NAP and the ISP is again required. Finally, as the network of FIG. 3 grows, additional IP addresses must be assigned. If the IP addresses of one of the two assigned 256-address subnets become exhausted, then either that subnet needs to be expanded to a larger one, or a new, possibly larger subnet assigned. It is observed that IP addresses remaining in the other subnet cannot be assigned or used in another part of the network (e.g., in another CO) because that would not allow IP routing to properly function. In either case, IP addresses need to be reassigned and reallocated, resulting in tedious subnet reconfigurations and IP network routing topology changes, all of which again must be coordinated between the NAP and the ISP. Additionally, IP address reassignments and reallocations can also require that subscribers reconfigure their equipment, and coordinate with their ISP and/or NAP.
Accordingly, a need exists for a technique which enables IP routing to be efficiently and conveniently implemented within high-speed broadband access networks. It is further desired that this implementation be effected without creating a large administrative or operational burden, and without necessitating significant coordination between generally unrelated entities (i.e., NAPs and ISPs).